Question

我想找到一种方法来确定是否使用C gnu11标准安装了一个程序，例如，如果使用C中的system函数执行命令'Rscript'将会工作吗？ / p>

我不是训练的prorgrammer，所以我不确定我是否使用了正确的搜索词。

我希望C等价于

con@con-Inspiron-3521:~/Scripts$ which Rscript 
/usr/bin/Rscript

我怎么能在C中做到这一点？

Answer 1

通过类似的工作，您只需解析PATH变量并检查给定文件是否存在且是否可执行：

#include <stdbool.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>

bool can_run_command(const char *cmd) {
    if(strchr(cmd, '/')) {
        // if cmd includes a slash, no path search must be performed,
        // go straight to checking if it's executable
        return access(cmd, X_OK)==0;
    }
    const char *path = getenv("PATH");
    if(!path) return false; // something is horribly wrong...
    // we are sure we won't need a buffer any longer
    char *buf = malloc(strlen(path)+strlen(cmd)+3);
    if(!buf) return false; // actually useless, see comment
    // loop as long as we have stuff to examine in path
    for(; *path; ++path) {
        // start from the beginning of the buffer
        char *p = buf;
        // copy in buf the current path element
        for(; *path && *path!=':'; ++path,++p) {
            *p = *path;
        }
        // empty path entries are treated like "."
        if(p==buf) *p++='.';
        // slash and command name
        if(p[-1]!='/') *p++='/';
        strcpy(p, cmd);
        // check if we can execute it
        if(access(buf, X_OK)==0) {
            free(buf);
            return true;
        }
        // quit at last cycle
        if(!*path) break;
    }
    // not found
    free(buf);
    return false;
}

Answer 2

程序可能会在PATH环境变量中指定的任何目录中搜索该文件。

有很多方法可以做到这一点，这就是一种方法

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <limits.h> #include <stddef.h> #include <sys/stat.h> int main(int argc, char *argv[]) { const char *head; const char *command; size_t length; if (argc < 2) { fprintf(stderr, "insufficient number of arguments\n"); return -1; } command = argv[1]; length = strlen(command); // Get the PATH environment variable head = getenv("PATH"); if (head == NULL) { fprintf(stderr, "the PATH variable was not set, what?\n"); return -1; } // Find the first separator while (*head != '\0') { struct stat st; ptrdiff_t dirlen; const char *tail; char *path; // Check for the next ':' if it's not found // then get a pointer to the null terminator tail = strchr(head, ':'); if (tail == NULL) tail = strchr(head, '\0'); // Get the length of the string between the head // and the ':' dirlen = tail - head; // Allocate space for the new string path = malloc(length + dirlen + 2); if (path == NULL) return -1; // Copy the directory path into the newly // allocated space memcpy(path, head, dirlen); // Append the directory separator path[dirlen] = '/'; // Copy the name of the command memcpy(path + dirlen + 1, command, length); // `null' terminate please path[dirlen + length + 1] = '\0'; // Check if the file exists and whether it's // executable if ((stat(path, &st) != -1) && (S_ISREG(st.st_mode) != 0)) { if ((st.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH)) == 0) { fprintf(stdout, "found `%s' but it's not executable\n", path); } else { fprintf(stdout, "found at: %s\n", path); } } // Don't forget to free! free(path); // Point to the next directory head = tail + 1; } return 0; }

一般来说算法相同

获取PATH环境变量，该变量由一系列由:字符分隔的目录路径组成。

通过迭代获取此序列中的每个目录路径，这是您可以通过多种方式完成的。

检查是否，

文件存在。

具有来电者的执行权限。

Answer 3

根据@Paul_R的回答，我想出了以下内容：

#include <stdio.h>
#include <linux/limits.h>//PATH_MAX definition
#include <string.h>//strlen
#include <stdbool.h>

const bool is_program_installed( const char *restrict COMMAND) {

    FILE *restrict fp;
    fp = popen(COMMAND, "r");
    if (fp == NULL) {
        pclose(fp);
        return false;
    }
    char path[PATH_MAX];
    bool return_value = false;
    while (fgets(path, PATH_MAX, fp) != NULL) {
         if (strlen(path) > 0) {
            return_value = true;
            break;
         }
    }
    pclose(fp);
    return return_value;
}

int main() {

    printf("ls  %s\n", is_program_installed("ls") ? "true" : "false");
    printf("not_program %s\n", is_program_installed("not_program") ? "true" : "false");
    return 0;
}

如果没有打印“sh：1：not_program：not found”，工作会很好，但这已经足够了。

检查程序是否安装在C中

3 个答案: